Translation of abstract (English)

The 'small glutamine rich TPR containing protein', SGT, has been identified as a cellular interaction partner of the autonomous parvovirus H1 main regulatory protein NS1. Upon infection SGT accumulates together with NS1 in APAR-bodies, the sites of parvoviral replication. Furthermore, it is modulated in a NS1 dependant manner. Taken together this indicated a possible role of SGT in the parvoviral life cycle. The data presented here show for the first time that SGT is needed for effective parvoviral replication. Drastic reduction in the amount of SGT by means of RNA-interference led to a significant decrease in viral replicative forms with the highest effect on single stranded virion DNA. These results imply that SGT is either directly involved in viral DNA replication or indirectly in processes which are connected to the viral replication such as packaging of the viral genome or capsid assembly. SGT has no impact on steps important for establishment of the viral infection e.g. virus adsorption, entry or viral protein expression. In neuronal cells SGT was found to be part of a chaperon complex together with CSP and Hsc70 and it was therefore tempting to speculate that such a complex could also function during parvoviral replication. Interestingly, Hsc70 was not detected in APAR-bodies, hence other chaperone proteins come into play. NS1 as well as two SGT binding proteins of 66 and 160kDa respectively, which have been identified in this study, are likely candidates. In addition, we attempted to map regions within SGT which are responsible for (1) NS1 interaction, (2) localization in APAR-bodies or (3) are subject to NS1 dependant modifications. Thereby the central TPR-domain and the N-terminus were shown to be sufficient for the interaction with NS1 while the location of SGT in APAR-bodies does not require the N-terminus of the protein. Concerning the NS1-induced modification it was shown that N-terminal serine and threonine residues of SGT become phosphorylated.